Manufacturers of arc-utilizing apparatuses are sometimes requested by customers to provide a power supply apparatus for the arc-utilizing apparatus having various output capacities. One example of solutions to such problems is disclosed in Japanese Patent Application Publication JP 08-001350 A laid open to public on Jan. 9, 1996.
According to the invention disclosed in this publication, an inverter-type resistance welder having standard capacity is used. The standard capacity resistance welder uses DC power obtained by converting commercial AC power in a converter circuit. The converted DC power is, then, converted to high-frequency power in an inverter, which, in turn, is coupled to a primary winding of a welder transformer having rectifying circuits in its secondary side. There are also provided an inverter control unit which controls the inverter, a synchronizing signal generating circuit which generates a synchronizing signal from a commercial AC power supply, and communication means. The inverter control unit controls the inverter in synchronization with the synchronizing signal from the synchronizing signal generating circuit.
A plurality of such standard capacity inverter-type resistance welders providing an output capacity corresponding to the output capacity required by a customer are provided, and outputs of the secondary sides of the welder transformers of the respective welders are connected in parallel. The communication means is connected through lines to the communication means of the other inverter-type resistance welders.
One of the inverter-type resistance welders is used as a master welder, and the other inverter-type resistance welders are used as slave welders. The master welder sends a synchronizing signal to the slave welders through the communication means, and the inverters of both the master and slave welders are controlled in synchronization with the synchronizing signal of the master inverter-type resistance welder.
Electromagnetic noise is generated due to arcing in an arc-utilizing apparatus. Accordingly, if the technique disclosed in JP 08-001350 A is employed for arc-utilizing apparatuses, electromagnetic noise may cause erroneous operation of the communication means, and, therefore, means to prevent such erroneous operation must be provided, which requires some costs.
An object of the present invention is to provide a power supply apparatus for arc-utilizing apparatuses, which employs unit-forming power supply blocks of standard capacity so as to meet various output capacities required by customers, but not includes communication means like the one described above for realizing the purpose.